I. Field
The following description relates generally to wireless communications, and more particularly to transmission precoding in wireless communications networks.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, . . . ). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP2, 3GPP long-term evolution (LTE), etc.
Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. Further, communications between mobile devices and base stations may be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or base stations with other base stations) in peer-to-peer wireless network configurations.
MIMO systems commonly employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. The antennas can relate to both base stations and mobile devices, in one example, allowing bi-directional communication between the devices oil die wireless network. The base stations can perform precoding of one or more signals to provide beamforming when transmitting the signals. Additionally, base stations (or mobile devices) can employ cyclic delay diversity (CDD) in the physical antennas to introduce spatial diversity into the frequency domain. Thus, a number of antennas can operate with an antenna-specific delay to transmit precoded signals with redundancy and diversity increasing successful decoding at the receiving end. However, since the CDD is applied in the physical antenna domain, in cases when the number of transmit antennas is greater than the number of receive antennas, data streams, or transmission layers, portions of transmission energy are poured into a null space, inaccessible by a receiver, negating many benefits of precoding.